A sign that's got a sting in the tail
I believe the answer is:
scorpion
'the tail' is the definition.
The definition and answer can be both animals as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'a sign that's got a sting' is the wordplay.
'a sign' becomes 'scorpio' (sign of the zodiac).
'that's got a sting' becomes 'n' (I can't explain this - if you can you should believe this answer much more).
'scorpio'+'n'='SCORPION'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for scorpion that I've seen before include "Poisonous arachnid" , "As above (Latin)" , "Venomous creature" , "Stinging arachnid - constellation" , "Eight sign of Zodiac, kind of spider" .)